Contest File Size

what makes you think that submission will be handled via steam workshop?

very true, i just checked my e-mail. disregard the above

It's called compression. Look at encoding it with a different codec.

500mb video is pretty big, see if it's truly a worthwhile addition. Don't forget, not everyone has a 1080 monitor yet. You should be ok with 720.

Again, with the right compression, smart editing and bitrate you should be able to reduce filesizes significantly.

I have one mission with quite a bit of voicework and it's under 2 megabytes. Half of that is audio, the rest mostly images. The longest sentence is about 30 seconds and is 130kb.

Unless you intend to put in full lossless music tracks you shouldn't getting near a gigabyte. Or you have way too much dialog in a lot of really long missions.